Contamination of both the saturated and unsaturated zones of the subsurface with volatile organic compounds (VOCs) is ubiquitous. The potential adverse health effects and other environmental implications of VOC contaminated subsurface systems has made remediation of these sites a major focus of environmental concern. At present, the most popular techniques for remediation of these contaminated sites is the application of physical mass transfer and concentration processes, e.g. vapor extraction of contaminated soil and gas stripping of contaminated ground water For example, U.S. Pat. No. 4,544,488 (O'Brien) is directed to gas stripping of contaminated ground water. O'Brien describes injecting VOC contaminated water and noncontaminated water into an induced draft air stripper through spray nozzles to strip the volatile organic contaminants from the water into the air stream. The VOC contaminated air stream is vented to the atmosphere and the effluent water stream is passed through a carbon adsorption bed for removal of nonvolatile organic contaminants
An unfortunate consequence of the vapor extraction and gas stripping treatment processes is the transfer of the volatile organic compounds from one medium to another, i.e. in many cases the off-gases of these processes is simply vented to the atmosphere without further treatment.
In addition, many manufacturing, fuel transfer and combustion processes discharge VOCs directly to the atmosphere. In many cases, discharges of VOCs to the atmosphere simply go untreated. Treatment of VOC contaminated gas streams, when applied, typically takes the form of a cost intensive nonrecoverable process such as an activated carbon adsorption process or a combustion Process. For example, U.S. Pat. Nos. 4,540,579 (Cunningham) and 4,343,096 (Berglund) are each directed to combustion processes for treating VOC contaminated gas streams. However, the high cost of combustion processes limits the applicability of combustion technology as a routine treatment for VOC contaminated gas streams.
The application of known off-gas treatment techniques to the removal of VOCs from a gas stream frequently proves economically and/or practically infeasible Activated carbon adsorption as described in "Using GAC To Remove VOCs From Air Stripper Off-Gas" J.C. Crittendent et al, J. American Water Works Association, 80:5:73, 1988 is a known off-gas treatment. However, the expense of online adsorption as well as the poor removal efficiencies for certain common VOC contaminants, e.g. methyl chloride and 1,1,1,-trichloroethane, limit the practical applicability of adsorption technology as routine treatment process for VOC contaminated gas streams.
Each of the above discussed treatment methods approach the problem of VOC contamination from a very limited perspective, i.e. treatment of a VOC contaminated medium regarded as a disposal problem, rather than as a potential source of a renewable resource.